Non-blocking coated sheet material



2,833,671 Patented May 6, 1958 fiice 2,833,671 NON-BLOCKING COATEDCSHEET MATERIAL Murry C. Funk, Menasha, and John F. Helms, Neenah, Wis, assignors, by mesne assignments, to American Can Company, New York, N. Y., a corporation of New Jersey Application May 22, 1956, Serial No. 586,541

7 Claims. (Cl. 117-76) This invention relates to improvements in non-blocking coating compositions and more particularly to non-- for example, have exhibited an undesirable stickiness or f tack on the surface of the coating. Rolls of the packaging materials tend to block so that it is impossible to unroll the material. Similarly, it is impossible to separate individual sheets of the packaging material when they havebeen stacked or piled one on top of another. Attempts have been made to overcome this disadvantage by interleaving the sheets or rolls with a non-blocking interleaving sheet which is separated and discarded at the time of use of the packaging material. The economic undesirability of such practice is obvious. sheet materials have also been dusted with starch to provide a non-tacky coating surface, butthe procedure involves operational difficulties because the starch. seriously impairs the heat-scalability of the wax composition coating, rubs off on the back of theadjacent sheet and serves also as a nutrient source for growth of molds and bac teria. Furthermore, it is very difficult to prevent the starch dust from entering the coating machinery an cleanliness is therefore diflicult to maintain.

By the practice of our invention, however, it is possible to achieve a non-blocking surface on normally tacky wax composition coatings applied to flexible sheet materials. This result is accomplished without the disadvantages attending previously used methods.

We have found that a non-blocking surface may be obtained by overcoating the wax composition with a composition containing a non-blocking agent and a material which acts as a binder to hold the non-blocking agent firmly on the surface of the coating. The non-blocking compositions of our invention are applied to the wax coinposition surface from solutions in suitable volatile solvents.-

The novel features of our invention, together with the advantages thereof, may best beunderstood from the following description of specific embodiments When read in connection with the accompanying drawing, in which numeral 1 designates a flexible base sheet material, such as a cellulosic sheet material or metallic or plastic film, numeral 2 designates a wax composition coating having a normallytacky or sticky surface and applied as a protective coating over the base sheet and numeral 3 designates thenon-blocking overcoating of our invention as applied over the surface of the tacky wax composition.

Our non-blocking overcoating composition may be applied to many types of known heat-scalable wax compositions which. are comprised of any suitable mixture of The coated c5 waxes and other ingredients such that the compositions are characterized by high surface tack and a tendency to block under the conditions of temperature and pressure normally encountered in storage of coated sheet materials. Wax compositions containing appreciable proportions of microcrystalline wax, polyisobutylene, unvulcanized rubber, petrolatum or similar materials fall in this category. Such compositions are often applied to flexible sheet materials for the preparation of protective wrappers for foodstuffs, particularly for natural and process cheese. A representative cheese wrapper coating composition might contain up to polyisobutylene and up to 15% petrolatum, the balance of the composition being microcrystalline wax. Various tacky resins may also be introduced to obtain special desired characteristics. The non-blocking overcoatings of our invention are of particular value when applied to the surface of wax compositions of this type, and are advantageous for. application on the surface of any similarly tacky wax composition.

The non-blocking agents useful in the preparation of our non-blocking overcoating compositions are solid, crystalline, organic compounds which are compatible, in the fused or molten state, with the underlying wax coating. They are applied to the wax coating surface from theirtsolution, together with a binder, in a volatile solvent which wets but does not attack or dissolve the wax coating. Upon evaporation of the solvent, the non-blocking composition remains on the wax coating surface. When heat is applied, as in the heat-sealing operations common to the packaging industry, the non-blocking agent fuses together with the wax coating and so contributes to the heat sealing qualities of the wax composition.

The non-blocking agents which we have found effective for use in our invention are the solid straight chain saturated fatty acids, solid hydrogenated castor oil and solid polyethylene glycols. Palmitic acid, stearic acid, Hydrofol Glyceride 200, which is a solid hydrogenated castor oil sold by the Chemical Products Division of Archer, Daniels, Midland Company, Castorwax, which is solid hydrogenated castor oil sold by the Baker Castor Oil Company, and Carbowax 6000W, a solid polyethylene glycol sold by Carbide and Carbon Chemical Corporation, have been found particularly effective in the practice of our invention.

The binding agent may be a cellulose ether such as Ethocel, which is ethyl cellulose sold by Dow Chemical Company, a polyvinyl acetate such as Gelva V7, which 'is polyvinyl acetate sold by Shawinigan Products Company, a polyamide such as Versamid 940, which is a polyarnide formed by reaction of a dimerizcd and trimerized unsaturated fatty acid with ethylene diamine and sold by General Mills, Inc., or other film-forming binding agents which are soluble in the preferred solvents hereinafter described.

The binding agent may generally comprise between about 2% and 15% by weight of solids in the non-blocking composition. Lesser amounts of the binder do not hold the non-blocking component securely to the Wax composition surface and it thereby tends to dust off,

' while higher percentages of binder are unnecessary and The non-blocking agents mentioned above may be used singly with the selected binding agent or mixtures of two or more of the non blocking agents in varying pro- 1.4 portions may be used in the preparation of the non-blocking coating composition of our invention. For example, hydrogenated castor oil, when used as the sole non-blocking agent, has excellent non-block characteristics, and can be used where mild heat-sealing qualities are required and a relatively opaque overcoat is desired. When hydrogenated castor oil is used in combination with palmitic acid or stearic acid, or a mixture thereof, however, excellent blocking resistance is. obtained together with excellent heat-sealing characteristics of the wax composition, and the coatings are transparent. The compositions containing stearic acid are less transparent than those which palmitic acid is used, so the former material is generally used when opaque coatings are desired, while Isopropyl alcohol and methyl ethyl ketone have proven to be excellent solvents for this use, though other solvents having similar properties may be employed quite satisfactorily.

To illustrate the principles of our invention, overcoating compositions as shown in the following Table I were prepared and applied to the surface of a cellophane sheet material coated with a normally tacky wax composition comprising polyisobutylene, 7% petroleum and 78% microcrystalline wax. The amount of the overcoating composition applied was sulficient to leave, after evaporation of the solvent, 4 lbs. (solid basis) per ream (3000 sq. ft.) substantiallyevenly distributed over the surface of the wax composition.

Table I Solids Ooncen- Resistance Heat Overcoat Solids Composition tration Solvent to Sealing in Blocking Quality, Solvent, percent i /zsgig if igiti :":3: gy q good good- 90 y o o yceri e sopropano O Gelva }30 {fi h f fizff }excellent fair.

9 Y }a0 Keme y do Do. 47:5% Palmitic Acid" }30 Isopropanol good good. 5% Ethocel- Hydrofol Glyceride 200 55% Palmitic Acid 30 do excellent.-- Do. 5% Ethocel 40% Hydrofol Glyceride 200 55% Oarbowax 6000W 30 do do Do. 5% Ethocel is generally used when opaque coatings are desired, while mixtures of these acids are used, the mixture is generally in the ratio of 10 partsby weight. of palmitic acid to between 1 part and parts by weight of stearic acid.

Solidunsaturated fatty acids also form similar noncompositions in relatively small amounts. For example,

when applied to the surface of a normally tacky wax composition such as is used for coating cheese wrappers, the application ofabout 4 lbs. per ream (3000 sq. ft.) of

one of our compositions resulted in a completely satisfactory non-blocking surface. Application of less than about 2.5 lbs. per ream gives incomplete blocking protection, while applicationjin excess of about 10 lbs. per

ream had a deleterious effect on the heat sealing qualities of the wax composition.

The overcoating compositions are preferablyapplied fronrsolvent solutions, the solvent being subsequently removed by normal evaporative techniques such as passing the sheet through an oven or over heated rolls. Solvent application results in an overcoating in the form of an essentially continuous film of substantially even thickness and permits an extremely close control of the weight of the overcoating composition which is applied to the substrate surface.

A variety of solvents maybe used for this purpose. To be satisfactoryin the use the solvent must: (1) have sufiicient volatility to be readily removed from the overcoated sheet material after application of the overcoating solution, (2) have sufficient solubility for the desired solid cvcrcoating components .to maintain them in solution at temperatures not unduly elevated above room temperature, (3) have sufiicient wetting power for the wax composition to allow the over-coating solution to spread evenly over the wax composition surface, and (4) be a non-solvent for the Wax-composition, at least at the temperature used for the overcoating application.

In the above table: Ethocel is ethyl cellulose sold by Dow Chemical Company. The grade used was termed 25 Centipoise, Standard Ethoxy.

Hydrofol Glyceride 200 is a solid, hydrogenated castor oil sold by the Chemical Products Division of Archer, Daniels, Midland Company.

Gelva V-7 is a polyvinyl acetate sold by Shawinigan petrolatum and 78% microcrystalline wax were over coated, in accordance with our invention, with a composition comprising palmitic acid, 40% hydrogenated castor oil and 5% ethyl cellulose. The overcoating was applied from a 30% solution in isopropanol. The overcoating was non-blockingttransparent and the overcoated Wrappers exhibited low surface friction and superior performance in machine packaging operations. Half pound portions of sliced process cheese were packaged in these wrappers on a vacuum packaging operating at 24-26 inches (Hg) of vacuum. The heat seals on the resulting vacuum-packed cheese packages were excellent, all packages maintaining a satisfactory vacuum for 6 to 9 months.

Similarly prepared wrappers were used to package 6 ounce portions of sliced bologna under about 25 inches (Hg) of vacuum. Heat seals were excellent, allpackages maintaining satisfactory vacuum for the 6'week duration of the test. t

Having now disclosed several of the preferred compositions of our invention and the method of their application, it is evident that various modifications may be made within the spirit of our invention. We do not wish to be limited in the interpretaton of our invention except as distinctly set forth in the appended claims.

We claim:

1. A flexible packaging sheet material coated with a heat-sealable normally tacky wax composition and overcoated with a non-blocking composition comprising a solid binding agent selected from the group consisting of ethyl cellulose, polyamides and polyvinyl acetate, and a non-blocking component selected from the group consisting of solid straight chain saturated fatty acids, solid hydrogenated castor oil, and solid polyethylene glycols, said solid binding agent being present in amount of at least 2 percent by Weight of the solids in the non-blocking composition.

2. A flexible packaging sheet material coated with a heat-sealable normally tacky wax composition and superimposed thereon a non-blocking overcoating in an amount between 2.5 lb. and lbs. per ream, said overcoating comprising between about 2% and about by weight of solids of a binding agent selected from the group consisting of ethyl cellulose, polyvinyl acetate and polyamides, and between about 85% and 98% by weight of solids of a non-blocking component selected from the group consisting of solid straight chain saturated fatty acids, solid hydrogenated castor oil, and solid polyethylene glycols.

3. A flexible packaging sheet material coated with a heat sealable normally tacky wax composition and overcoated with between about 2.5 lbs. and 10 lbs. per ream of a non-blocking composition comprising between 2% and 15% by weight of ethyl cellulose, between and 60% hydrogenated castor oil and between 30% and 75% solid straight chain saturated fatty acid.

4. A flexible packaging sheet material coated with a heat scalable normally tacky wax composition and overcoated with between about 2.5 lbs. and 10 lbs. per ream of a non-blocking composition comprising between 2% and 15% by weight of ethyl cellulose, between 20% and solid hydrogenated castor oil, and between 30% and palmitic acid.

5. A flexible packaging sheet material coated with a heat sealable normally tacky wax composition and overcoated with between about 2.5 lbs. and 10 lbs. per ream of a non-blocking composition comprising between 2% and 15% by weight of ethyl cellulose, between 20% and 60% hydrogenated castor oil and between 30% and 75% of a mixture of palmitic and stearic acids, said mixture being in a ratio of 10 parts by weight of palmitic acid to between 1 part and 50 parts by weight of stearic acid.

6. A flexible packaging sheet material coated with a heat scalable normally tacky wax composition and overcoated with between 2.5 lbs. and 10 lbs. per ream of a non-blocking composition comprising between 2% and 15% by weight of ethyl cellulose and between and 98% by weight of palmitic acid.

7. A flexible packaging sheet material coated with a heat-sealable normally tacky wax composition and overcoated with between 2.5 lbs. and 10 lbs. per ream of a non-blocking composition comprising between 2% and 15% by weight of ethyl cellulose and. between 85% and 98% by weight of solid hydrogenated castor oil.

References Cited in the file of this patent UNITED STATES PATENTS 2,319,957 'Speicher May 25, 1943 2,339,200 Sowa Jan. 11, 1944 2,447,506 Jubanowsky Aug. 24,1948 2,603,576 Cook et al. July 15, 1952 2,750,302 Camarda et a1 June 12, 1956 

1. A FLEXIBLE PACKAGING SHEET MATERIAL COATED WITH A HEAT-SEALABLE NORMALLY TACKY WAX COMPOSITION AND OVERCOATED WITH A NON-BLOCKING COMPOSITION COMPRISING A SOLID BINDING AGENT SELECTED FROM THE GROUP CONSISTING OF ETHYL CELLULOSE, POLYAMIDES AND POLYVINYL ACETATE, AND A NON-BLOCKING COMPONENT SELECTED FROM THE GROUP CONSISTING OF SOLID STRAIGHT CHAIN SATURATED FATTY ACIDS, SOLID HYDROGENATED CASTOR OIL, AND SOLID POLYETHYLENE GLYCOLS, SAID SOLID BINDING AGENT BEING PRESENT IN AMOUNT OF AT LEAST 2 PERCENT BY WEIGHT OF THE SOLIDS IN THE NON-BLOCKING COMPOSITION. 